The embodiments described herein are particularly well suited for use in, and offer very significant benefits to, the rapidly developing wind power industry. The United States and other nations throughout the world are striving to develop ways of producing electrical power from sources other than fossil fuels, and one of the most popular alternatives is to utilize wind energy to drive wind turbine generators. Unfortunately the present state of the art of generating electrical power from wind energy is such that in many parts of the world, and particularly in the United States, wind power is not economically competitive with the more traditional methods of generating power from fossil fuels. It is believed that for wind power to become widely utilized, methods must be developed to reduce the cost per unit of electrical power generated to where it is equal to, or less than, that resulting from the use of fossil fuels. One way of accomplishing this is to find a way of more economically erecting the wind turbine generators at the desired high elevations where the winds are more ideal and the turbines perform more effectively.
The embodiments of the present invention described herein provide methods and apparatus that make the erection, use, and maintenance of large high towers more efficient and for some selected applications possible when they might otherwise not be possible.
Windmills and various types of wind turbines have been used for many years to pump water, generate electricity and provide power for numerous other purposes. Initially these windmills and turbines were typically mounted at the top of lattice types of towers, which were usually built from straight structural steel members assembled into a configuration having a rectangular cross section and four legs on the outside corners that extended from the ground to the top of the tower. Various types of horizontal and diagonal braces were used to stabilize the column-like legs so they would stay straight and not buckle in side-ways directions. Lattice types of towers are frequently seen in photographs or paintings of windmills on farms in the late 1800s and early 1900s.
U.S. Pat. No. 133,017 discloses a telescoping lattice type signal tower for use in elevating a human observer or signalman in a basket-like apparatus fixed to the top of the tower. The tower was actuated, or extended upward through a system of cables and pulleys. The cables and pulleys are burdensome and add overall cost to the system.
Small telescoping towers that were extended upward by filling them with compressed air are disclosed in U.S. Pat. No. 1,264,063 wherein mast consisting of telescoping round tubes is used for hoisting telecommunications antennas to relatively low heights. Masts of this type are clearly not suitable for elevating large heavy objects to high heights. In addition, the tower described therein required shrouds, or guy wires, to provide the tower with side ways stability. More importantly, the mast required continuous pressurization throughout the time it was to be extended.
Another telescoping tower that was extended by compressed air is described in U.S. Pat. No. 1,325,053. It was primarily for use on submarines, required continuous air pressure throughout the time it was extended, and was obviously made by utilizing precisely machined components and was thus difficult and expensive to manufacture and use.
U.S. Pat. No. 4,137,535 discloses a telescoping antenna mast that was operated by pneumatic, or air, pressure. This mast is lightweight and is obviously not suited or adaptable for elevating large equipment such as a wind turbine or the like. Further, no provisions are described for securing the sections in the extended position once extended such as by fastening, and the telescoping antenna requires continuous air pressure throughout the time it is extended, the sections appear to be fully machined, and the tower is not strong enough to withstand the lateral and bending loads imposed by large wind turbines.
U.S. Pat. No. 6,955,025 discloses a tower that is hinged at mid-height and required a large, very expensive crane to unfold it outward and upward until it was straight up and down and is therefore not self-erecting.
U.S. Pat. No. 4,594,824 describes a lightweight tower that is not designed or suited for elevating large heavy equipment such as a wind generator. It requires expensive machining, and there are no provisions for bolting or otherwise securing the sections together after they are extended, wherein air pressure must be continuously supplied to maintain the tower in an elevated conformation. The bottom portion of the various sections are without rigidity such as would be necessary for the tower to have the lateral bending resistance required for wind tower use.
The current state of the art in wind generator towers is a tower consisting typically of three cylindrical sections, each having a size of about 12 to 14-ft in diameter and about 90 feet long, either tapered or progressively smaller in diameter than the section below it, and weighing about 60 tons. These sections are lifted into place by a huge, extra-heavy lift crane and set on top of each other end to end and then bolted together. The typical wind turbine generator assembly weighs about 60 tons and is lifted up and set on top of the erected tower, typically at vertical elevations of about 300 ft high. This erection requires at least one extremely expensive, huge, extra-heavy lift crane. Such cranes are typically brought in sections to the tower erection site by 50 or more heavy-haul semi-trucks. The cost of buying, transporting, assembling and dismantling these cranes is extremely high. By eliminating the need for such cranes, the present invention greatly reduces the cost of erecting the tower and wind turbine generator, which in turn lowers the cost of producing electricity from wind energy and makes the widespread use of wind energy more likely in the near future.
U.S. Pat. No. 6,782,667 B2—Henderson, Aug. 31, 2004; and Patent Application Publication #US2005/0005562 A1—Henderson et al, Jan. 13, 2005 clearly illustrate the great cost of using the extra-heavy lift cranes to erect large wind turbine generators. These represent attempts to advance the state of the art in wind towers by constructing the towers of telescoping sections, and in the case of U.S. Pat. No. 6,782,667 by also hinging the bottom end of the lower section and tilting the towers up into a vertical configuration after nesting the sections in the horizontal position. In the second case, a lift mechanism interconnecting the sections is needed, and the erection method cited begins with mounting the outer lower section on the foundation whereas the assembly sequence for the present invention begins with setting the innermost section on the foundation and setting the outer section last.
U.S. Pat. No. 6,470,645 issued Oct. 29, 2002 to Maliszewski relates to wind towers that are designed with thicknesses and braces including a conical transitional section between the upper and lower sections in such a way as to diminish certain vibrational characteristics that can threaten the strength of the tower. Like the other types of wind towers typically being used today, these towers also require a huge, very expensive extra-heavy lift crane to erect them.
Several types of “hybrid” wind towers have been disclosed such as in U.S. Pat. Nos. 7,276,808 and 7,694,473 for example, with the primary feature of these towers being the use of a larger diameter lower section of the tower that is made of concrete or a lattice type of structure. A more typical steel wind tower is then normally set on top of, and attached to, the lower base section in order to have a tower that goes higher into the air than a totally steel tower can. Totally steel towers that are higher than about 290 feet are not economical to produce since in order to have adequate strength the walls must be made extra thick if the maximum diameter at the bottom is maintained at 14 ft. so they can be shipped by truck or rail. Again, a huge, very expensive extra-heavy lift crane is required to erect the hybrid towers. Also, it should be noted that the telescoping air-extended tower of the present invention is fully compatible with the hybrid types of towers.
Although the previously discussed patents and other published developments show the art relating to the design and construction of large, tall towers used to support machinery and devices such as wind turbine generators, tower cranes, communications equipment and advertising signs at substantial heights above the ground includes towers that telescope and small telescoping pneumatic towers that are maintained in an extended position by a continuous source of injected pressurized air applied to the tower, the art does not teach, suggest or disclose large, tall, telescoping towers for supporting big, heavy items such as wind turbine generators such as the tower described herein that can be extended to its full height simply by pumping compressed fluid such as water, air or a mixture of water and air into its interior, maintaining such pressure only until the tower sections are mechanically or otherwise secured, and then returning the interior of the tower to normal atmospheric pressure. The art further fails to teach, suggest or disclose an ability to lower such a tower and the load it supports simply by reversing the procedure used to erect it. The methods of making and using the self-erecting tower and the embodiments of the tower described in connection with example embodiments make it unnecessary to use a huge, extra-heavy lift crane, or cables and winches, hydraulic cylinders, jacks, or other types of mechanical devices to construct or erect the tower to its full height, or lower its load after the tower has been erected.